Preset frequency rejection in intermediate frequency amplifiers



S R E l F T. L P. .M A Y C N E U Q E R F E T A m mm w m m E v N I N O T.. T C E J E R v.. C N E U Q E R F T E s E R P l 4 9 l 9 2 n a J d e. l .1 F

i l l l l l 1 r l Gmo ,Bardem Vl lllllllhlllxllxlfwlll... T m JIET n R f |M. IL LdwQ/'..

F lllllllllllllllllll |.IL

- ,Tuning to the desired peak frequency will accomplished lry varying Ci and Cz.

IParental Dea-1,1942

rnEsE'r FREQUENY REJr-:c'rloN 1N MER- l MEnrA'rE FREQUENCY .aMPLlFmns l Emerick Toth, Cheverly, Md.

Appiiaauoaranuaryzs, 1941, serial No. 316,408 'v s claims. (ci. 17a-44) a (Granted undertiia aat atomaren a, isss. as amended April 30, 1928; 370 0. G.- 757) This invention relates to al tuned amplifier circuit arranged to automatically reject certainl undesired frequencies in the neishborhoodof the peak frequency of the circuit. It is an object of this invention to provide such acircultwhich will be automatically tuned to'a predetermined Fig. 2 is a view similar tothe.: shown in Fig. 1

l' showing the circuit arranged to reject a frequency below thepeak frequency of the circuit, and

similar to that shown in Fig. 1 but arranged for rejection both above andy belowthe peak frequency.

Fig. 3 is adiagrammatic view Aor the circuit` In the drawing reference characters Vi and Vav y.

refer to a pair of amplifier tubes, the plate cir-v cuit of V1 being coupled to the grid circuit of Vi by means of an I. F. coupling device or transformer having a secondary L4 and a primary La. The reference character Ti indicates the complete coupling circuit.

The primary La lies in one branch of a tuned '4 factured and/or used by or for the Government circuit containing inductance Li and capacitance C1 in its other branch. The circuit branch LiCi is tuned to the desired rejection frequency. 'Ihe secondary L4 vlies in one branch of a similar circuit, theother branch vbeing formed by inductance La and variable capacity Ca.. The circuit branch LaCz is tuned to the same frequency as,

LiCi or to another desired rejection frequency. Both frequencies must lie above the peak frequency of the I. F. transformer. The values of Li and Ci must be lchosen to resonate at the desired rejection frequency, and must have a combined reactance at the I.'F. peak frequency that will be capacitive and of such value as to resonate with La at the I. F. peak frequency. Thus LiCi will eifectively bypass La at the rejection frequency and will tune it to parallel resonance at the peakfrequency. The same will be true of InCz and Li. L: and L4 can be coupled `to the degree desired for the peak'band width required in the I. F. amplifier system. This coupling may be inductive or capacitive or both.

In Fig. 2' is shown a circuit arrangement for peak frequency ofthe transformer. LiCi and L'zCz again form the rejector circuits, La and Li having been'replaced by capacitors C: andV C4v tuning with the equivalent inductive reactance of LiCi and LiC-z respectively at the I. F. peak frequency. 4C5 provides the coupling capacity neces-rl l V sary for the band width required.

Fig. V3 shows a circuit arrangement for combined rejection below and above peak frequency. In this circuit LiCi forms the rejector circuit lfor a frequency above peak frequency and IrrCzy forms a rejector circuit for a frequency below peak frequency. La is an inductance resonating Y with the equivalent capacity reactance of LiCi at peak frequency and C4 is a capacitor resonating with the equivalent inductive reactance of LzCz at the peak frequency. C5 is a coupling capacitor. Y

The required shielding is shown in the figures by dotted lines.

By use of the circuits shown, the transformer is automatically tuned to the predetermined rejection frequency or frequencies when it is peaked by adjusting Ci and C: at the peak frequency.

While the disclosure has been restricted to three embodiments, the invention ls not to be considered as limited therebyA but only'by the scope and limitations of the appended claims.-

'I'he invention described herein may be manuof the United States of America for governmental purposes without the payment of any royalties onant coupling means having one inductive and one capacitive element, means for rejecting a pair of undesired frequencies in the neighborhood of the peak vfrequency of said coupling means, one of said undesired frequencies being above and the other of said frequencies being below the said peaklfrequency of saidcoupling means, comprising a tuned circuit shunted across each element of said coupling means, each of said tuned circuits being tuned to one of said re.'V

a rejection frequency or frequencies below the selected as to have at the peak frequency of'said coupling means, a. combined reactance which is across a voltage source ioadrespectiveiy."

inductive in nature and of such value as to resone or said branches in each of said circuits cononate with said capacitive element of said coutaining one of said inductances and said capacipling means. tor, said one ci said inductances and said capaci- 2. In an I. F. amplifier circuit including a res- 5 tor being resonantA at a predetermined frequency onant coupling means having a pair of inductnear said peak frequency.

ances as'elementsgmeansafor rejecting` apair; of .f5..Infan-I-. Ff,ampliiiercircuitaii1ter, assemundesired frequencies in the neighborhood fof-z' andi'C blyy comprising` ajjpair {of} pled circuits resoabove the peak frequency of said coupling means, nant at the predetermined peak'frequency of said comprising a tuned circuit shunted across each e119-, qfllter, a pair of capacitors and an inductance inof said elements of said coupling means, eachof x each of said circuits, means dividing each of said said tuned circuits being tuned'to onc",v `K c "i rcuins-ifiitoftwo'par'allel branches across a voltjection frequencies, the L. C. values' f""each" ofy ages'ourcelandf'a'l load respectively, one of said -said tuned circuits being so selected asgtogghgvegfg- A fiira .n y:,hes,V inieach of said circuits containing one -assembly comprising a-,pair `oit coupledfcircuits capacitor ineach of said circuits, means 'dividing each of said circuits into two parall at the peak frequency of said coupling means, `L15 of said capacitors and said inductance, said one combined reactance which is capacitive ilnature Vff-fofsaidcapacitors?` and said inductance being res and of such value as to resonate with saideie.- i 0n3nt .t-=a predetermined frequency near said ment of'said coupling means across which alii-11" peak'irquency.

tuned circuit is shunted. "i: :6: "Incan 1. flgampliiler circuit, a lter assem- 3. In an I. F. amplifier circuit including afr'esi?` k26 bly 4for, .'useffas-mplate load for a vacuum tube of onant coupling means having av.y pairoicapacitcrs said circuit comprising a first circuit and a sec.

as elements, means forrejecting onefor'a` pmi-lof7 or'idjgcircuitjcupled;thereto?saidcircuitsffbeing undesired ,frequencies in the: neighborhood of and.A r'gggan'jgc be1owA the peak frequency` of said c'uplins Ineens,y ofsaidi nite comprising a -tunedmcircuitfshuntd jacross each 5 @di Saidiulied Circuits BeingfiilediiSiiilfiecii?! soe"'eb bran he atacan' one frequencmtheL. Cavalues of-eachbf said tuned *ge .f v3 i circuitszbeinaso selectedlas to have, `aitiiepeak said second cimit imv two purine; Manages across/a iosdzf-onewamd ...hanches Vone oi' said-:capacitorscand said thef f predetermined .peak .frequency resonant at'thepredeterminedfpeak frequenti of one* f" sBid Mmmm l said transformer, a pair of inductances andfa resonant aegmpvredetlemmed frequency MQW requency l.

@1: 'brass @o 

